Warming

Given the fact that most cryotanks are contaminated, it should be assumed that samples withdrawn from cryotanks for warming or thawing can be contaminated also.

It has been demonstrated in numerous animal models, that the technique of multiple washing procedures is very effective in decreasing infectivity and in rendering oocytes or embryos free from many viral and bacterial pathogens (Stringfellow DA, Seidel S. Manual of the International Embryo Transfer Society, 3rd edn. Savoy, IL, USA: IETS, 1998.)

Additional washing of embryos after thawing or warming will likely facilitate a further decrease in their infectivity and reduce risk of cross-contamination between samples during cryobanking.

A method is now available for the cleansing of carriers stored in contaminated dewars. A paper by Parmegiani et al, describes a simple protocol for the cleansing of samples prior to thawing or warming. The protocol utilizes the technique of multiple washings and uses sterile Liquid Nitrogen as the washing medium. The study proves that three washings of the samples, that take no longer than 2-3 mins per sample, are sufficient to completely remove bacteria with which the samples had been contaminated. Since the bacterial load used in the study is much higher than the bacterial load likely to be found in cryotanks, it can be assumed that the protocol is equaliy effective in cleansing samples that may have become contaminated during storage in dewars.